This invention relates to a thin-film transistor (TFT) matrix for use in an active matrix display panel, such as a liquid-crystal display (LCD).
LCD active matrix display panels, which are employed in personal television sets and portable computers, comprise a pair of glass substrates enclosing a liquid crystal. The lower glass substrate has a matrix of TFTs that are switched on a row at a time by scanning signals applied to their gate electrodes. Image signals are applied to the drain electrodes of the TFTs, which are interconnected in the column direction. The source electrodes are connected to transparent electrodes that drive individual picture elements (pixels) of the display. A color display can be produced by providing red, blue, and green filters on the upper glass substrate.
In TFTs in prior-art active matrix display panels, the gate electrodes are formed from a thin tantalum film, the surface of which is anodized to create a gate insulator film. A problem arises in that the tantalum film has a comparatively high resistivity of 150 to 200 .mu..OMEGA..cm. The high resistance of the gate electrodes tends to distort the scanning signals, leading to display defects, such as uneven brightness and uneven color rendition. This problem is particularly acute in high-resolution liquid-crystal panels having a large number of pixels. Due to the large RC time constant of the gate electrodes near the terminating end of the scanning signal lines and the large distortion of the scanning signals during propagation, the TFTs do not all turn on promptly, so in addition to the brightness and color differences noted above, the display on one side of the panel responds sluggishly as compared with the other side of the panel.